1. Field of the Invention
This invention relates to a slider of a slide fastener comprising a slider body and a lug molded integrally by die casting, to which a pull tab is secured subsequently. It also relates to a metal mold for molding the same.
2. Prior Art
A slider of a slide fastener of the type under consideration has to be securely combined with a pull tab in a later stage of manufacturing. For securing a pull tab to the slider, a ring of the pull tab is introduced into the space between the arched lug and the slider body through the gap between a rear pillar of the lug and an upper wing of the slider body and then a front pillar of the lug is plastically deformed and bent toward the upper wing typically by means of a pincher. Thus, a slide fastener of this type can be realized by combining a slider body and a pull tab selected from a variety stocks to meet the demand of the consumer.
Meanwhile, a metal mold for producing a slider of the above identified type comprises an upper mold for defining the profile of the upper half of the upper wing and that of the lug, a lower mold for defining the profile of the lower half of the lower wing and an intermediary mold for defining the profiles of the remaining portions of the upper and lower wings and a so-called diamond section (guide post) as typically described in Japanese Utility Model Application Laid-Open No. 2-12889, of which the upper and lower molds include respective first and second (left and right) mold halves, whereas the intermediary mold includes first and second (front and rear) mold halves.
The lower mold has an U-shaped cross section with a groove formed at the center, into which the intermediary mold is placed. The first and second mold halves of the intermediary mold can slide back and forth between the upper and lower molds, whereas the first and second mold halves of the upper and lower molds can be moved laterally to open and close the mold assembly.
Known sliders of the type under consideration are accompanied by a drawback that, when the pull tab is brought into the space between the lug and the slider body and the front pillar is bent down for plastic deformation in order to securely anchor the pull tab, the front pillar can give rise to a fissure. It is very difficult to completely prevent such a fissure from taking place even if a rigorous quality control system is in place because of variations in the molded material and the molding conditions. Additionally, if the front pillar is properly deformed, there can occur a spring back phenomenon in it to produce a significant gap between the upper surface of the upper wing and the rear pillars. If the front pillar is bent downward with enhanced pressure to eliminate the gap, then not only can the front pillar be damaged but it can press to the upper surface of the upper wing at the lower end to deform the latter and damage the internal passage for the elements of the fastener and hence the commercial value of the fastener.
Meanwhile, known metal molds for molding sliders of the type under consideration comprise quite a number of components that have to be machined accurately to raise the manufacturing cost of the mold, while such a mold cannot be used for molding a large number sliders because of its durability. Additionally, each of the components is required to operate in a complex manner with timings that can be very complicated. Thus, the net result will be a high manufacturing cost of the fastener.
In view of these circumstances, it is therefore an object of the present invention to provide a quality slider for a slide fastener that is free from the above identified problems including the possible damage of the lug that can occur when the front pillar of the lug is pressed and deformed, the problem of spring back and that of a deformed upper wing and also to provide a metal mold for molding sliders of slide fasteners that has a simple structure and can be used for manufacturing a large number of sliders at low cost to improve the productivity.